High input impedance mixed-mode biquad filter with orthogonal tune of natural frequency and quality factor

This paper deals with a single-input multiple-output mixed-mode second-order filter providing two voltage-mode functions (low-pass and band-pass) and three transconductance-mode functions (low-pass, band-pass and band-reject) based on voltage differencing transconductance amplifier (VDTA). The quality factor and pole frequency can be electronically and orthogonally tuned via the bias current. The proposed circuit uses two VDTAs and two grounded capacitors without any external resistors, which is suitable to further develop into an integrated circuit. Moreover, the circuit possesses high input impedance, providing easy cascading. The PSPICE simulation results are included, verifying the key characteristics of the proposed filter. The given results agree well with the theoretical presumptions.